Concentration of liquid food products by evaporation is conducted at low temperature to avoid imparting a boiled flavor to foods such as milk or juices. Even pasteurization tends to be conducted at relatively low temperature. In the United States, pasteurization is carried out at 72.degree. C. (161.degree. F.) for 15 seconds or even at 62.degree. C. (143.degree. F.) for 30 minutes. In Europe, pasteurization is carried out at an even lower temperature of 57.degree. C. (135.degree. F.). The highest temperature utilized for pasteurization (161.degree. F.) is cooler than the hot-well of a power generation unit and cooler than most steam condensates. Therefore, with a good system, pasteurization could be accomplished with waste heat from power generation or other processes requiring higher temperatures.
Many of these fluids are further concentrated after pasteurization. Obviously, one would not want to repasteurize the liquid product again and again during concentration. The liquid product can be concentrated and cooled after pasteurization by conventional flash evaporation rather than passage through cooling coils. However, flash evaporators are not energy efficient.
MacDowell et al (U.S. Pat. No. 2,453,109) is an example of vacuum concentration of fruit juices. Barlow (U.S. Pat. No. 3,024,117) feeds a small particle size fog or mist into a vacuum chamber containing inert gas under conditions such that ice crystals are formed. Harlow et al (U.S. Pat. No. 4,101,681) distills coffee oil in a vacuum chamber is and condenses a desired coffee aroma fraction on a chilled surface.
Toulim, Jr. I (U.S. Pat. No. Re. 23,958) relates to a method and apparatus for vacuum dehydration of fruit and vegetable juices and the like by forming ice crystals. Note particularly that Column 2 commencing with line 19 and continuing through line 44, teaches multiple step freeze dry concentration processes. Toulmin, Jr. II (U.S. Pat. No. 2,916,386) combines the steps of freezing a liquid to be concentrated to produce progressively smaller crystals and then to shock freeze the concentrate in the process of forming a concentrate. Note Column 3 commencing with line 17 where a vacuum step may also be employed to vaporize ice.
Toulmin, Jr. III (U.S. Pat. No. 2,957,773) discloses in Column 2 commencing with line 14, the process whereby heated juice is sprayed into a chamber in the form of a fine mist, said chamber being maintained under sub-atmospheric pressure and temperature to form ice. Barr, Sr. et al (U.S. Pat. No. 3,276,848) and Stout (U.S. Pat. No. 3,892,662) disclose processes which provide for the use of freeze drying-vacuum distillation of sprayed droplets to recover potable water from body wastes. Ganiaris (U.S. Pat. No. 4,069,947) teaches concentration of aqueous solutions with the primary object being centrifuge means for recovering additional solids from ice.
All of these references operate below the triple point of water and/or direct a spray horizontally, outwardly, onto a chilled surface to form frost or ice.